The present invention relates to a cylinder servo motor having integrated therein a controller, a detector, a servo motor, a ball screw nut, and a ball screw shaft.
FIG. 14 shows a related-art cylinder servo motor. As shown in the drawing, reference numeral 63 designates a motor serving as a drive source; 64 designates a rotational speed detector for detecting the rotational speed of the motor 63; 68 designates a ball screw shaft; 67 designates a ball screw nut engaged with the ball screw shaft 68; and 65 designates a hollow cylinder rod. A load is connected to a load-side end 65a, and an opposite end 65b of the cylinder rod 65 is fastened to the ball screw nut 67. A rotary shaft bearing 82 is fitted around an end 68a of the ball screw shaft 68. A motor shaft 63a and the end 68a of the ball screw shaft 68 are coupled together by means of a flexible coupling 70. Reference numeral 77 designates an inner ring fastening nut. The inner ring fastening nut 77, along with an outer ring fastening nut 76 screw-engaged with an inner peripheral wall of a cylinder case 66, fixes the rotary shaft bearing 82. The cylinder rod 65 is supported by a sleeve shaft bearing 83 which is fastened to a load-side end 66a of the cylinder case 66 and has an oil seal 84. A slide block 69 is fastened to the cylinder rod 65 and is clearance-fitted to a keyway 66b formed in the cylinder case 66. Reference numeral 71 designates a case, which secures the cylinder case 66 and a motor case 72 that houses and supports the motor 63. Reference numeral 78 designates a hole formed in the case 71; and 79 designates a blank cap. Reference numeral 73 designates a cover of the rotational speed detector 64; and 74 designates a cable of the rotational speed detector 64. Reference numeral 80 designates a power line of the motor 63; 75 designates an amplifier serving as a controller; and 81 designates a higher-level controller.
In the related-art cylinder servo motor having the foregoing construction, power is fed to the motor 63 by way of the amplifier 75 in accordance with an instruction output from the higher-level controller 81, thereby rotating the motor shaft 63 and the ball screw shaft 68. Rotation of the cylinder rod 65 fastened to the ball screw nut 67 is stopped. Hence, the cylinder rod 65 does not rotate in conjunction with rotation of the ball screw shaft 68 and rotates directly along with the ball screw nut 67, thus acting as a cylinder servo motor.
The related-art cylinder servo requires the cable 74 for connecting the rotational speed detector 64 and the amplifier 75, and the power line 80 for connecting the motor 63 with the amplifier 75. The cable 74 and the power line 80 are wired by a machinery manufacturer or an end user. Hence, there sometimes arise problems, such as an operation failure or a failure of the rotational speed detector 64 due to incorrect wiring.
The motor shaft 63a of the motor 63 and the end 68a of the ball screw shaft 68 are coupled together by means of the flexible coupling 70. The coupling 70 requires the case 71, and there must be ensured a space in the axis of ball screw shaft 68, thereby increasing the overall length of the cylinder servo motor.
Since the ball screw shaft 68 is inserted into the cylinder rod 65, only a ball screw shaft which is smaller in diameter than the cylinder rod 65 can be used as the ball screw shaft 68. Hence, if an attempt is made to increase allowable thrust, the cylinder servo motor becomes bulky.
Since the cylinder rod 65 is supported by the sleeve shaft bearing 83, wear arises in the slide section as a result of sliding friction. Particularly, at the time of high-speed operation, the life span of the cylinder serve becomes shorter.
Further, the rotation of the cylinder rod 65 is stopped by means of the slide block 69 clearance-fitted to the keyway 66b. Hence, a contact surface of the cylinder rod 65 is abraded by means of sliding friction, thereby resulting in an increase in backlash.
Contact between the slide block 69 and the keyway 66b arises in the form of sliding friction. Hence, at the time of operation, excessive thrust corresponding to a friction loss in the contact surface is required, thus deteriorating efficiency.
Further, at the time of assembly of a cylinder servo motor, the motor shaft 63a and the end 68a of the ball screw shaft 68 are coupled together by the flexible coupling 70. A set screw (not shown) is fastened to the flexible coupling 70, by use of a hexagonal wrench and by way of a hole 78. To this end, the cylinder rod 65 must be moved along the axis of the ball screw shaft 68, thereby finding a hole for the set screw. This results in an increase in the number of assembly steps, thereby adding to costs.
The present invention has been conceived to solve the drawback of the invention and is aimed at providing a cylinder servo motor capable of eliminating a necessity of wiring operation.
The present invention provides a compact cylinder servo motor which can produce large thrust and a long linear stroke.
The present invention is also aimed at providing an efficient cylinder servo motor having a long life span.
The present invention is also aimed at providing a cylinder servo motor which is superior in ease of assembly.
A cylinder servo motor according to the present invention comprises:
a servo motor having a rotor and a stator;
a cylinder servo motor main unit which is connected to a rotary shaft of the rotor of the servo motor by way of a ball screw nut and which has a ball screw shaft, the ball screw shaft moving in an axial direction;
a rotation sensor for detecting a rotary position of the servo motor; and
control means for controlling the rotation sensor and the servo motor, wherein
the cylinder servo motor main unit, the rotation sensor, and the control means are mechanically integrated;
the rotor of the servo motor is constituted of the rotary shaft and a permanent magnet, the rotary shaft being rotatably supported by a load-side bearing supported by a load-side bracket and by a non-load-side bearing supported by a non-load-side bracket, at least the load-side end of the rotary shaft being released, a through hole being formed in the rotary shaft so as to extend in an axial direction, and the permanent magnet being disposed opposite the stator fixed to the rotary shaft with a predetermined clearance therebetween;
the ball screw nut is constituted of a ball circulation mechanism and is mounted on a load-side shaft end of the rotary shaft;
the ball screw shaft is screw-engaged with the ball screw nut so as to become movable in only the axial direction such that a non-load-side shaft end of the ball screw shaft is housed in the through hole of the rotary shaft and such that a load-side end of the ball screw shaft protrudes from the load-side bracket;
a rotation portion of the rotation sensor is coupled to a non-load-side portion of the rotary shaft protruding from the hole formed in the non-load-side bracket and is covered with a rotation sensor cover;
the control means is disposed on a part of the non-load-side bracket distant from the stator; and
the control means and the rotation sensor cover are covered with a chassis to be fastened to the non-load-side bracket.
A necessity of wiring a line between the servo motor, the rotation sensor, and the control device section at a location to which the cylinder servo motor is to be shipped is obviated, thereby improving workability. As a result, a wiring failure, which otherwise is apt to arise at a location to which a cylinder servo motor is shipped, is prevented. Further, the wiring operation is obviated, thereby improving workability.
Since there is obviated use of any coupling for coupling a rotary shaft with a ball screw shaft, which would have hitherto been employed, the cylinder servo motor becomes compact despite having a long stroke. Hence, the cylinder servo motor is made compact overall, and the number of components is reduced.
The rotation portion of the rotation sensor is doubly covered with the rotation sensor cover and the chassis. Accordingly, reliability of the cylinder servo motor against an external environment is improved.
According to the present invention, the non-load-side end of the rotary shaft and the through hole are elongated to a position where the control means of the servo motor is disposed. Further, in association with elongation of the non-load-side end and elongation of the through hole, the non-load-side shaft end of the ball screw shaft is elongated.
Hence, there can be obtained a cylinder servo motor which, for a given dimension, has a stroke of comparatively long linear movement.
Further, in the cylinder servo motor according to the present invention, a non-load-side of the through hole of the rotary shaft is opened, and a cover for covering the open side is removably provided. Further, a through hole is formed in a portion of the chassis opposing the cover with reference to an axial direction of the rotary shaft. Moreover, the through hole formed in the chassis is removably provided with a cover.
Accordingly, there can be effected manual positioning of the ball screw shaft while the cylinder servo motor is mounted on a machine, thereby improving workability and operability. At this time, since the cylinder servo motor is provided with a cover for covering the open section of the rotary shaft and a cover for covering a through hole formed in the chassis, good reliability of the rotation section of the rotation sensor against an external environment is achieved.
In the cylinder servo motor according to the present invention, the load-side shaft bearing is constituted of a ball bearing. An outer ring of the ball bearing is fixedly sandwiched between a shoulder section formed on an internal peripheral wall of the load-side bracket and an outer ring fastening nut to be screw-engaged with an internal peripheral wall of the load-side bracket. An inner ring of the ball bearing is fixedly sandwiched between a ball screw nut fastening shoulder section formed on the load-side shaft end of the rotary shaft of the servo motor and an inner ring fastening nut to be screw-engaged with the rotary shaft of the servo motor. An inner diameter of the inner ring of the ball bearing is made greater than an outer diameter of the rotor of the servo motor.
As a result, assembly of a cylinder servo motor from one direction becomes possible, thereby improving workability.
In the cylinder servo motor according to the present invention, the ball screw nut fastening shoulder is formed on the load-side shaft end of the rotary shaft, and a fastening flange section is formed on the ball screw nut. A portion of the ball screw nut is fitted into the through hole formed in the load-side shaft end of the rotary shaft. The fastening flange section is brought into contact with and screw-engaged with the ball screw nut fastening shoulder section. Thereby, the ball screw nut is fastened to the load-side shaft end of the rotary shaft, and an oil seal is held on the load-side bracket. A lip section of the oil seal is brought into contact with an outer peripheral surface of the ball screw nut fastening flange.
As a result, the oil seal section can be shortened in an axial direction thereof, thereby rendering the cylinder servo motor more compact.
In the cylinder servo motor according to the present invention, a ball screw nut fastening shoulder is formed on a load-side shaft end of the rotary shaft, and a fastening flange section is formed at a position closer to the center of the ball screw nut. A portion of the ball screw nut is fitted into a through hole section formed in the load-side shaft end of the rotary shaft, and the fastening flange section is brought into contact with and screw-engaged with the ball screw nut fastening shoulder section. As a result, the ball screw nut is fastened to the load-side shaft end of the rotary shaft, and an oil seal is held on the load-side bracket. A lip section of the oil seal is brought into contact with an outer peripheral surface at the shaft end of the ball screw nut.
A sliding diameter of the lip section of the oil seal becomes smaller, and a circumferential speed of a contact section becomes smaller. Hence, abrasion resistance of the oil seal is improved, and the life span of the cylinder servo motor is extended.
In the cylinder servo motor according to the present invention, a detent groove is formed in an outer peripheral section of the ball screw shaft, wherein the detent groove has substantially the same depth as that of a thread groove or a depth shallower than that of the thread groove and extends in an axial direction. Further, the ball screw shaft has at least two balls to be inserted into the detent groove, and a spring for pressing the balls toward the detent groove at all times. The balls are disposed such that at least one of the balls is situated in the detent groove at all times.
Hence, the whirl stop makes rolling contact. Accordingly, abrasion of the contact surface is reduced, prolonging of the life span of a whirl stop, and friction loss of the whirl stop is diminished (by extension, input power is diminished, thereby realizing energy savings).
In the cylinder servo motor according to the present invention, a detent groove is formed in an outer peripheral section of the ball screw shaft, wherein the detent groove has substantially the same depth as that of a thread groove or a depth shallower than that of the thread groove and extends in an axial direction. Further, the ball screw shaft has at least one cylindrical ball which is to be inserted into the detent groove and is larger than a screw pitch of the ball screw shaft, and a spring for pressing the cylindrical ball toward the detent groove at all times.
Hence, one detent unit provided in the direction of the rotary shaft acts as a whirl stop. Accordingly, there can be obtained a cylinder servo motor having a shorter overall length.